Lamp base



FIG. 1 is a perspective view of a lamp base showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a bottom plan view thereof; and,

FIG. 4 is a top plan view thereof.

The broken lines in FIG. 1 are shown for illustrative purposes only. 

The ornamental design for a lamp base, substantially as shown and described. 